The Cesium-137 Irradiator Facility provides gamma irradiation of animals, cultured cells. microorganisms and other biological materials. Dosimetry and radiation chemistry reactions are also appropriate applications. The Facility has Mark I irradiator, Model 68 (J.L Shepherd and Associates, Inc.) It contains two Cesium-137 sources with activities of 6,000 and 100 curies, respectively. Its specific features include: . A large, fixed cavity (12" wide and 14" high) with a controllable environment (temperature, humidity, atmospheric gases). . A wide range of dose rates from 0.11 cGy/min without a significant reduction in cavity size. . Four access tubes for electrical leads, heating or cooling media, controlled airflow, etc. . A variable slit collimator system which allows partial irradiations without a significant reduction in cavity size. . Redundant safety interlocks to prevent radiation exposure of personnel, and an integrated radiation alarm that monitors the area constantly.